This invention relates generally to the field of angiogenesis and cancer therapy and more specifically to the use of superfibronectin and superfibronectin-generating compounds for the amelioration of pathologies with angioproliferative components, tumor cell growth and tumor metastasis.
Metastasis accounts for most deaths in cancer patients with solid tumors. The extent of tumor cell adhesion to the extracellular matrix and the stimulation of angiogenesis are critical steps in the metastatic process. Metastatic potential depends upon a complex series of events, including interactions of malignant tumor cells with extracellular matrix. Cellular adhesion to the extracellular matrix is primarily mediated by integrins, cell surface receptors which comprise an expanding family of transmembrane heterodimers of an .alpha. and a .beta. subunit. The identity of the subunits usually determines the receptor's functional specificity.
Several lines of evidence indicate that integrins play a key role in the malignant behavior of neoplastic cells. First, it has been demonstrated that integrin expression can change following viral or oncogenic transformation and that such alterations can affect the regulation of cellular protease cascades and tumor progression. Second, overexpression of .alpha.5.beta.1 in Chinese hamster ovary cells and of .alpha.2.beta.1 in human breast carcinoma cells has been shown to suppress tumorigenesis. Giancotti, F. G., et al., Cell 60:849-859 (1990). Third, inhibition of tumorigenicity and metastasis has been observed upon selective blocking of integrin function by RGD-containing peptides, which mimic integrin ligand binding sites. Inhibition of tumorigenicity and metastasis has been observed upon selective blocking of integrin function with function-blocking antibodies against individual .alpha. and .beta. subunits. Finally, the heterologous expression of the .alpha.2 subunit in RD human rhabdomyosarcoma cells has been shown to profoundly alter their metastatic pattern, while the transfer of .alpha.4 into murine B16 melanoma cells suppressed their ability to produce pulmonary metastasis. Chan, B. M. C., et al., Science 251:1600-1602 (1991).
The steps of the metastatic process in which integrins may play a role include detachment from the primary tumor and penetration of adjacent extracellular matrices and blood vessels; interaction with platelets and leukocytes in the circulation; and arrest and extravasation in the target organ. Giancotti, F. G., et al, Biochem. Biophys. Acta 1198:47-64 (1994).
One of the most important integrin ligands and a major component of extracellular matrix is fibronectin. Superfibronectin (sFN) is a polymeric fibrillar form of fibronectin which may be related to the natural matrix form of fibronectin. Compared to fibronectin, sFN has greatly enhanced cell adhesive properties. Whereas cells attach to fibronectin through integrins, cell attachment to sFN is mediated by both integrins and other distinct receptors. sFN can be produced in vitro by the incubation of fibronectin with fibronectin fragments. Morla, A., et al., Nature 367:193-196 (1994).
The growth of solid tumors and the metastatic process is dependent on vascularization of the tumor, a process called angiogenesis. Angiogenesis involves cytokine-mediated activation of blood vessel endothelial cells. Endothelial cells so activated are capable of forming entire capillary networks. In humans, a tumor which is not able to stimulate its own vascularization, i.e. is not angiogenic, may for years be restricted in growth to a few mm.sup.3 and be limited to a million or less cells in size. Stimulation of blood vessel growth, i.e. the conversion of a tumor to an angiogenic phenotype, involves a change in the local balance of blood vessel growth inhibitors and growth stimulators. In addition to allowing a tumor to increase in size, this ingrowth of blood vessels also provides a means for tumor cell metastasis. Therefore, there is a need for factors which inhibit endothelial cell growth and angiogenesis, thereby having an antitumor effect by inhibiting tumor growth, causing tumor regression and inhibiting metastasis.
Factors which inhibit the growth and migration of endothelial cells can be used to treat diseases with angiogenic components, such as ocular neovascularization due to macular degeneration, diabetic retinopathy, rheumatoid arthritis, psoriasis, granulomas, granulation tissue and the like. Factors which inhibit the growth and migration of endothelial cells can also be used to inhibit or cause regression of the growth of tumors of the blood vessels, such as hemangiomas, sclerosing angiomas, Kaposi's sarcoma, lymphangioma, glomangioma, angiosarcoma, hemangio-endotheliomas and the like.
There thus exists a need for agents for therapeutic intervention which can be used in the treatment and inhibition of angiogenesis, tumor growth and metastasis. This invention satisfies these needs and provides related advantages as well.